Distinct calcium-independent and c systems of chicken embryo cells

Three criteria have been used to distinguish among different systems of embryonic cell adhesion: dependence on Ca2+, involvement of particular cell-surface molecules, and binding specificity. The characterization of the adhesion with re- spect to cell-surface molecules was carried out by using specific antibodies against the neural and liver cell adhesion molecules (N- CAM and L-CAM) and antibodies raised against retinal cells pre- pared by limited trypsinization in the presence of Ca2+ (called "T/ Ca cells"). Aggregation of cells prepared from retina or brain with- out Ca2+ did not require Ca2+ and was inhibited by anti-(N-CAM) antibodies but not by anti-(L-CAM) or anti-T/Ca cell antibodies. In contrast, cells obtained from the same tissues in the presence of Ca2+ did require Ca2+ to aggregate. This aggregation was inhib- ited by anti-T/Ca cell antibodies but not by anti-(N-CAM) or anti- (L-CAM) antibodies. Hepatocyte aggregation also required Ca2+ and was inhibited only by anti-(L-CAM) antibodies. These results define three antigenically distinct cell adhesion systems in the em- bryo and raise the possibility that additional systems will be found. The neural Ca2+-independent system displayed a limited tissue specificity, mediating binding to neural but not liver cells. In con- trast, the Ca2+-dependent systems of both neural and liver cells adhesion molecule (N-CAM) and liver cell adhesion molecule (L-CAM) (11). The two CAMs are antigenically distinct. The present study is concerned with a comparison of the ag- gregation of retina, brain, and liver cells prepared by different tissue-dissociation techniques (10-13) that have been shown to give calcium-dependent and calcium-independent adhesion (13-18). We have examined these cell types with respect to the involvement of particular cell adhesion molecules in the bind- ing process, and the ability of the different cell types to bind to each other. The results suggest the presence of at least three distinct adhesion systems during development: a calcium-in- dependent and a calcium-dependent system in neural cells and a different calcium-dependent system in liver cells. These find- ings are related to studies by other workers and are discussed in terms of their significance in organogenesis.